He played his initial first-class match for Marylebone Cricket Club (MCC) as early as 1921, but his potential was not noticed until 1924, when he began qualifying by residence for Gloucestershire.
Though he did not accomplish anything remarkable, Sinfield was very consistent and reached a thousand runs every year from 1927 until 1935, in the process carrying his bat through an innings on five occasions – the most significant being when he scored 161 not out in a total of 374 against Oxford University in 1931.
His most notable feat was nine wickets for 111 against some extremely aggressive Middlesex batting at Lord's – according to Wisden that record "fully demonstrated his steadiness" – and only Goddard's return prevented Sinfield taking all ten.
When first-class cricket resumed in 1946 Goddard continued his devastating form for several years, but Sinfield took immediately to coaching at Clifton College and Colston's School.
During this period, he championed a number of future Test players, notably Chris Broad, and only retired in his mid-eighties, two years before his death on 17 March 1988 in Ham Green, North Somerset.